Vascular occlusions are blockages of the cardiovascular system (which includes both coronary and peripheral vessels) that significantly or completely block the flow of blood through the vessel. The progression of the disease state that causes vascular occlusions, generally referred to as atherosclerosis involves the gradual deposition of fatty, fibrous and/or calcific deposits along the interior wall of the vessel. This progression may occur slowly, sometimes taking a number of years. Vascular occlusions may be categorized as “functional” or as a Chronic Total Occlusion (CTO). The occlusions are functional, for example, when the vessel has developed significant stenosis that blocks the majority of blood flow, but a small finite pathway remains through the vessel. The occlusions are categorized as CTOs when the progression of the disease state has completely occluded the vessel and has stopped all flow of blood through the vessel at the point of the occlusion.
In arterial disease, often as the lumen of the native vessel begins to slowly close, the tissue served by this native vessel becomes ischemic and the body may respond by generating angiogenic factors that initiate the growth of new “collateral” vessels that originate proximal to the site of the occlusion and feed the tissue distal to the occlusion. These new vessels may help to stabilize the tissue's requirement for blood flow and oxygen during rest or nominal activity. These collateral vessels may occur in both the coronary and peripheral vasculature. However, often these new collateral vessels cannot sustain an adequate delivery of blood and oxygen to the tissue under more demanding situations such as exercise. For blockages in peripheral vessels such as in the legs, the patient may develop clinical symptoms such as claudication in the legs (pain while exercising), or in the case of coronary blockages the patient may develop shortness of breath or chest pain while exercising.
The physical treatment of vascular occlusions may involve interventional methods (for example, non-surgical, catheter based methods), or surgical methods. The intent of interventional treatment is to re-cannalize the occluded vessel by first generating an initial small pathway through the occlusion, and subsequently radially expanding the small pathway via balloon angioplasty to a diameter that is nominally equal to the original diameter of the vessel prior to its becoming occluded. The site may also be treated with athrectomy catheters and stents as well to facilitate the long term patency of the vessel.
Interventional treatment typically involves introducing a specialized wire, referred to as a guide wire, into the vessel that is proximal to the occlusion and advancing the guide wire using fluoroscopic means through the occlusion and into the vessel that is distal to the occlusion. This fundamental technique may be practiced in both coronary (heart) vessels and peripheral (for example, iliac, superficial femoral, sub-clavian) vessels. Once the guide wire is delivered through the occlusion and into the vessel lumen distal to the occlusion, a balloon catheter may be delivered over the guide wire to perform balloon angioplasty at the site of the occlusion.
However, conventional guide wires are not designed for generating pathways through total occlusions. Rather they are designed with very flexible distal terminations to allow them to typically navigate through non-occluded but stenosed vessels, for the purpose of the subsequently delivery of a balloon catheter to perform angioplasty at the site of the stenosed artery. The design of a guide wire capable of generating a pathway through a total occlusion is a challenging task, whereas the guide wire must be robust enough to pass through the occlusive material, but also be friendly enough so as not to perforate through the vessel wall, should the guide wire not take a direct path through the occlusion. However, the divergence of the guide wires pathway through the occlusion is a clear possibility, since the composition of a total occlusion can be very non-homogeneous, leading to the guide wires deflection off of fibrous or hard calcific deposits, leading to its potential advancement through the vessel wall, which is clearly undesirable.
Interventional methods to treat vascular total occlusions can be challenging and problematic, and present high risk factors, as described above. As such, patients presenting with vascular total occlusions are frequently referred directly to the surgical method of treatment. Alternatively, patients are frequently referred to surgical methods following the failure of an interventional attempt. While the surgical approach is clearly more traumatic to the patient, the actual mechanics of the procedure are more straightforward the procedure is generally accepted as having fewer complications.
In the surgical approach, an external conduit is used to bypass the occlusion, wherein one end of the conduit is attached to the vessel proximal to the occlusion, and the other end of the conduit is attached to the vessel distal to the occlusion. In this way, the flow of blood is re-routed around the occlusion. The conduit may be an explanted section of artery or vein, or may be a man-made conduit, typically fabricated of a Dacron composition.
The surgical approach however is also not without complications. Whereas the surgical approach generally results in favorable clinical outcomes, it is very invasive as compared to the interventional approach and subsequently leads to a much greater recovery period for the patient. Consequently, in reviewing the surgical and interventional approaches to treating chronic total occlusions, it is evident that a non-surgical approach would be desirable, and an improved interventional treatment would be further desirable that could increase success rates and lessen the complications associated with present interventional procedures.
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